The Aguas Do Douro Paiva Company (ADDP) responsible for assuring the water supply to the City of Oporto, submitted a particularly difficult task to Culligan: that of filtering large quantities of water from Douro River without the use of any chemical products.

The pre-existing yet recently constructed water treatment plant had often been unable to cope with the turbidity peaks of the Douro, leading to drastic decreases in capacity and serious problems to the regular supply of water to the City.

A solution therefore needed to befound for water filtration to ensure that a constant treated water quality even when river water reaches turbidity peaks of 200 NTU. There were two critical factors in the project: the first was the prohibition of chemical products for disinfection and flocculation (which would require separate treatment for filter backwashing water before it could be released into the river); the second was the lack of information on the actual nature and dimensions of turbidity particles. The supplier would therefore be required to ensure a qualitatively constant result, without being fully acquainted with the conditions in which the plan would be operating. Several water tretment companies invited for test studies including Culligan. At the conclusion of the test period, Culligan was chosen for the contract, having been the only company to have passed the tests conducted. The contract awarded to Culligan and inaugurated on 3rd November, 2003.